Effects of organic carbon source, chemical oxygen demand/N ratio and temperature on autotrophic nitrogen removal

To assess the feasibility of the Anammox process as a cost-effective post-treatment step for anaerobic sewage treatment, the simultaneous effects of organic carbon source, chemical oxygen demand (COD)/N ratio, and temperature on autotrophic nitrogen removal was studied. In batch experiments, three operating conditions were evaluated at 14, 22 and 30 °C, and at COD/N ratios of 2 and 6. For each operating condition, containing 32 ± 2 mg NH4(+)-N/L and 25 ± 2 mg NO2(-)-N/L, three different substrate combinations were tested to simulate the presence of readily biodegradable and slowly biodegradable organic matter (RBCOD and SBCOD, respectively): (i) acetate (RBCOD); (ii) starch (SBCOD); and (iii) acetate + starch. The observed stoichiometric NO2(-)-N/NH4(+)-N conversion ratios were in the range of 1.19-1.43, and the single or simultaneous presence of acetate and starch did not affect the Anammox metabolism. High Anammox nitrogen removal was observed at 22 °C (77-84%) and 30 °C (73-79%), whereas there was no nitrogen removal at 14 °C; the Anammox activity was strongly influenced by temperature, in spite of the COD source and COD/N ratios applied. These results suggest that the Anammox process could be applied as a nitrogen removal post-treatment for anaerobic sewage systems in warm climates.